get ID inside a Silverlight Datagrid when Button clicked

This blog pots describes a datagrid and a encapsulated custom button for each row. I want to show two methods how to get information about the underlaying data of the row.

I use a ado.net data service and a entity datamodel, which is not part of the article, to get the data. Database is good old northwind and table is customer. When use clicks on button messagebox comes up with some information about the row.